Hydraulic fracturing is a common stimulation technique used to enhance the production of hydrocarbon fluids from subterranean formations. In a typical hydraulic fracturing treatment, fracturing treatment fluid containing a solid proppant material is injected into the formation at a pressure sufficiently high enough to cause the formation to fracture or cause enlargement of natural fractures already present in the reservoir. The fracturing fluid that contains the proppant or propping agent typically has its viscosity increased by a gelling agent such as a polymer, which may be uncrosslinked (linear) or crosslinked, and/or a viscoelastic surfactant. During a typical fracturing treatment, propping agents or proppant materials are deposited in a fracture, where they remain after the treatment is completed. After deposition, the proppant materials serve to hold the fracture open, thereby enhancing the ability of fluids to migrate from the formation to the well bore through the fracture. Because fractured well productivity depends on the ability of a fracture to conduct fluids from a formation to a wellbore, fracture conductivity is an important parameter in determining the degree of success of a hydraulic fracturing treatment and the choice of proppant may be critical to the success of stimulation.
Because the proppants must hold the fracture open, traditional proppants are made from very strong and/or crush-resistant materials. Suitable traditional proppants include, but are not necessarily limited to, white sand, brown sand, ceramic beads, glass beads, bauxite grains, sintered bauxite, sized calcium carbonate, walnut shell fragments, aluminum pellets, nylon pellets, nuts shells, gravel, resinous particles, alumina, minerals, polymeric particles, and combinations thereof. It will be appreciated that since relatively large amounts of proppants are often used in a proppant stage that it is important to consider ways of reducing the cost of proppants.
Proppant-like deformable particles have also been used in conjunction with proppants for various purposes, for instance, in order to minimize proppant flow back problems.
Proppant has also been used for gravel pack operations. Gravel packing is a sand-control method employed to prevent the production of formation sand. Gravel packing treatments are used to reduce the migration of unconsolidated formation particulates into the wellbore. Typically, gravel pack operations involve placing a gravel pack screen in the wellbore and packing the surrounding annulus between the screen and the wellbore with gravel designed to prevent the passage of formation sands through the pack. The gravel pack screen is generally a type of filter assembly used to support and retain the gravel placed during the gravel pack operation. Particulates known in the art as gravel are carried to a wellbore by a hydrocarbon- or aqueous-based carrier fluid, including viscosified or brine-based systems. The carrier fluid leaks off into the subterranean zone and/or is returned to the surface while the particulates are left in the zone. The resultant gravel pack acts as a filter to separate formation sands from produced fluids while permitting the produced fluids to flow into the wellbore.
In some situations the processes of hydraulic fracturing and gravel packing are combined into a single treatment to provide stimulated production and an annular gravel pack to reduce formation sand production. Such treatments are often referred to as “frac pack” operations. In some cases, the treatments are completed with a gravel pack screen assembly in place, and the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In such a situation, the hydraulic fracturing treatment usually ends in a screen out condition creating an annular gravel pack between the screen and casing. This allows both the hydraulic fracturing treatment and gravel pack to be placed in a single operation.
It would be desirable to provide a method and material for proppants that give choices of less expensive and/or alternate materials which may nevertheless be suitable for proppants. It would also be desirable to provide proppants of relatively low density and/or low specific gravity.